全文获取类型
收费全文 | 69898篇 |
免费 | 6118篇 |
国内免费 | 4677篇 |
专业分类
化学 | 23431篇 |
晶体学 | 185篇 |
力学 | 4001篇 |
综合类 | 1107篇 |
数学 | 33373篇 |
物理学 | 18596篇 |
出版年
2024年 | 104篇 |
2023年 | 571篇 |
2022年 | 964篇 |
2021年 | 1871篇 |
2020年 | 1626篇 |
2019年 | 1787篇 |
2018年 | 1473篇 |
2017年 | 1477篇 |
2016年 | 1773篇 |
2015年 | 1680篇 |
2014年 | 2701篇 |
2013年 | 4946篇 |
2012年 | 2935篇 |
2011年 | 3652篇 |
2010年 | 3468篇 |
2009年 | 4256篇 |
2008年 | 4409篇 |
2007年 | 4549篇 |
2006年 | 3644篇 |
2005年 | 2990篇 |
2004年 | 2671篇 |
2003年 | 2628篇 |
2002年 | 4956篇 |
2001年 | 2255篇 |
2000年 | 1829篇 |
1999年 | 1635篇 |
1998年 | 1541篇 |
1997年 | 1224篇 |
1996年 | 1074篇 |
1995年 | 864篇 |
1994年 | 844篇 |
1993年 | 747篇 |
1992年 | 725篇 |
1991年 | 552篇 |
1990年 | 484篇 |
1989年 | 374篇 |
1988年 | 385篇 |
1987年 | 298篇 |
1986年 | 309篇 |
1985年 | 436篇 |
1984年 | 339篇 |
1983年 | 203篇 |
1982年 | 387篇 |
1981年 | 560篇 |
1980年 | 496篇 |
1979年 | 532篇 |
1978年 | 417篇 |
1977年 | 315篇 |
1976年 | 266篇 |
1973年 | 167篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
111.
112.
用能量法求多自由度振动系统的角频率 总被引:2,自引:1,他引:1
利用简谐振动能量方程,通过分析振幅矢量的关系,用能量法求多自由度振动系统的角频率或简正振动频率。 相似文献
113.
Ludmila C. Fidale Sarah Köhler Martin H.G. Prechtl Thomas Heinze Omar A. El Seoud 《Cellulose (London, England)》2006,13(5):581-592
The concentrations of water, W, and electrolytes present in solutions of LiCl in N,N-dimethylacetamide, LiCl/DMAc, and of tetrabutylammonium fluoride. x-hydrate in DMSO, TBAF.xW/DMSO can be accurately and expediently determined by three independent methods, UV–vis, FTIR and EMF measurement. The first relies on the use of solvatochromic probes whose spectra are sensitive to solution composition. It is applicable to W/LiCl/DMAc solutions but not to TBAF.xW/DMSO, because the charge-transfer complex bands of the probes are suppressed by strong interactions with the latter electrolyte. Integration of νOH band of water may be employed in order to determine [W], hence [electrolyte] by weight difference. EMF measurement uses ion-selective electrodes in order to determine [electrolyte], hence [W] by weight difference. Results of the latter method were in excellent agreement with those of FTIR. The reason for the failure of Karl Fischer titration is addressed, and the relevance of the results obtained to functionalization of cellulose under homogenous solution conditions is briefly commented on. 相似文献
114.
As borders between different entities, lines are an important element of natural images. Indeed, the neurons of the mammalian
visual cortex are tuned to respond best to lines of a given orientation. This preferred orientation varies continuously across
most of the cortex, but also has vortex-like singularities known as pinwheels. In attempting to describe such patterns of
orientation preference, we are led to consider underlying rotation symmetries: Oriented segments in natural images tend to
be collinear; neurons are more likely to be connected if their preferred orientations are aligned to their topographic separation.
These are indications of a reduced symmetry requiring joint rotations of both orientation preference and the underlying topography.
This is verified by direct statistical tests in both natural images and in cortical maps. Using the statistics of natural
scenes we construct filters that are best suited to extracting information from such images, and find qualitative similarities
to mammalian vision.
PACS84.35+i 89.70.+c 87.57.Nk 相似文献
115.
116.
本文对任意正整数n界定了矩阵方程X A*X-nA=I的正定解的特征值的范围,给出了它的极大正定解一个充分条件. 相似文献
117.
P. E. Cladis 《Journal of statistical physics》1991,62(5-6):899-925
We first discuss nonlinear aspects of phase transition theory applied to a particular liquid crystal phase transition. A simple derivation is given to show how two coupled Goldstone modes (one appearing as gauge fluctuations of the ordered phase) can force a phase transition, against all expectations, to take place discontinuously (theory of Halperin, Lubensky, and Ma)-but the discontinuity may be immeasurably small. Then, we describe a new dynamical test of phase transition order, developed by Cladiset al., that turns out to be more sensitive than x-ray diffraction and adiabatic calorimetry. Quantitative data found by this new method are in excellent agreement with the measurements of adiabatic calorimetry and x-ray diffraction as well as expectations implicit in the predictions of HLM.This is the text of an after-banquet talk given at the CNLS Workshop on the Dynamics of Concentrated Systems. 相似文献
118.
Summary In this paper a Gauss-Jordan algorithm with column interchanges is presented and analysed. We show that, in contrast with Gaussian elimination, the Gauss-Jordan algorithm has essentially differing properties when using column interchanges instead of row interchanges for improving the numerical stability. For solutions obtained by Gauss-Jordan with column interchanges, a more satisfactory bound for the residual norm can be given. The analysis gives theoretical evidence that the algorithm yields numerical solutions as good as those obtained by Gaussian elimination and that, in most practical situations, the residuals are equally small. This is confirmed by numerical experiments. Moreover, timing experiments on a Cyber 205 vector computer show that the algorithm presented has good vectorisation properties. 相似文献
119.
This paper reports that the m-plane GaN layer is grown on (200)-plane LiAlO2 substrate by metal-organic chemical wpour deposition (MOCVD) method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer's thickness. The high transmittance (80%), sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at -3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate. 相似文献
120.
E. A. Bailov N. Temirgaliev 《Computational Mathematics and Mathematical Physics》2006,46(9):1515-1525
Sharp estimates (in the power scale) are obtained for the discretization error in the solutions to Poisson’s equation whose right-hand side belongs to a Korobov class. Compared to the well-known Korobov estimate, the order is almost doubled and has an ultimate value in the power scale. 相似文献